The best chance to create counterplay. Caruana undoubtedly had prepared this move in advance.
3. a1b3  3... b8a6 Caruana keeps the c7-pawn protected. 4. d2d3  4... c7c6 Forever preventing Nb5, but the position of the knight on b6 is weakened. 5. c1e3 Immediately exploiting the problems with Black's last move.